According to The Featherweight 221 and I, (I know you have a 222, but I think the principle is the same) a stray thread that gets into the Bobbin area of the machine wraps itself around the bobbin carrier and because of the close fit of the parts, can bog the machine down or even lock it up.
First you have to remove the throat plate by taking out the two screws (dont lose them) Remove the bobbin case. Then remove the gib screw, a tiny screw at about 5 if you were looking at a clock face - need a very small screwdriver for this. (don't lose this one either, its worth its weight in gold)
The Gib will roll out the side of the bobbin case carrier (to the right) There is a screw at the end of the gib that comes in from the back side of the carrier and the gib rotates out on that screw. Turn the bobbin case until the point on its edge is just below the tip of the sewing hook. Only in this position can the bobbin case carrier be removed or reinstallled. Remove the carrier and look for dust and some stray thread. Clean it all out and put a little oil in before you close things up again.
You could really do with the accompanying diagrams, but perhaps if you give your repair man this info, it might help him.
Final instruction is to make sure that when replacing the throat plate, do not forget to put the positioning finger (for the bobbin case) back into the vertical slot on the underside of the throat plate. Best of luck.